The invention relates to a method and to a system for setting the electrical characteristics of a microelectronic circuit configuration in which the circuit configuration has at least one analog electronic unit. The invention also relates to using a microelectronic circuit element for setting the characteristics of such a circuit configurations.
The design of microelectronic circuit configurations, in particular those circuit configurations which have both analog electronic units and digital units, is one of the most demanding tasks in current electrical engineering. Although simulations are normally carried out before the production of the circuit configurations, a fault-free design cannot be guaranteed. The consequences of faulty designs are, inter alia, the time-consuming and costly search for errors, the repeated production of expensive masks for the production of the microelectronic circuit configurations and the redesign of the circuit configuration.
In microelectronic circuit configurations, programmable logic devices (PLDs) have been used for some time. The PLDs include, amongst others, PLAs (programmable logic arrays), PAL (programmable array logic) and FPGAs (field programmable gate arrays). The common factor to PLDs is that digital units can be linked differently in order to process digital information, that is to say they can be programmed. In particular, FPGAs in this way permit the prior hardware checking of designs of digital circuit configurations. FPGAs comprise a large number of configurable logic blocks and a network of lines, which can provide virtually any required pattern of connections between the blocks. For this purpose, switches, which can be actuated by external signals, are available at the crossing points of the lines.
U.S. Pat. No. 5,563,526 discloses a programmable circuit configuration having both digital and analog circuit units. In addition to the possibilities already offered by FPGAs, the analog characteristics of the analog units can also be changed, and the analog units can be linked with one another and/or with the digital units in different ways.
For example, U.S. Pat. No. 5,563,526 discloses an analog unit which can be programmed both as a comparator and as an operational amplifier. To this end, the analog unit has a programmable switch which, when it is closed, permits operation as an operational amplifier and, when it is open, permits operation as a comparator.
As in the case of the FPGAs, however, it is not possible for the analog electrical characteristics of the components of such a unit to be changed, for example, the gain of a transistor in the amplifier circuit or the resistance of a component. The possibilities of employing designs of mixed microelectronic circuit configurations is therefore restricted to a few applications, which have to be taken into account in advance in the circuit configuration.
It is accordingly an object of the invention to provide a method and a system for setting the electrical characteristics of a microelectronic circuit configuration which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to make it possible to set analog electrical characteristics of the circuit configuration continuously, that is to say to be able to select from a continuous value range. It is a further object of the present invention to provide a method of using a microelectronic circuit element with which the aforementioned objective may be achieved.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of setting electrical characteristics of a microelectronic circuit configuration, which includes a step of providing a microelectronic circuit configuration having at least one analog electronic unit. In a configuration step, an electrical charge is moved in a manner selected from the group consisting of feeding the electrical charge and extracting the electrical charge and thereby puts the analog electronic unit into a state that permanently determines analog electrical characteristics of the analog electronic unit so that the circuit configuration can be operated using these analog electrical characteristics. The configuration step is performed at a time selected from the group consisting of a time before operating the circuit configuration and a time during operation of the circuit configuration.
In other words, in a configuration step before or during the operation of the circuit configuration, by feeding and/or extracting electrical charge, the analog unit is put into a state which permanently determines the analog electrical characteristics of the unit, so that the circuit configuration can be operated using these characteristics. As a result, the charge state of the analog unit, in particular the charge state of a region which is electrically insulated during operation, is set to a charge value which lies within a continuous s value range. In this way, in turn, the electrical field strength is defined which originates from the region that is generally charged up. In microelectronic components, this means exerting an influence on the electrical characteristics of adjacent regions, so that the adjacent regions belonging to the analog unit have specific characteristics which depend on the field strength. The circuit configuration can be operated using these specific characteristics.
In accordance with an added feature of the invention, the analog unit has a microelectronic circuit element with a floating gate. In the configuration step, the floating gate is charged up to any desired charge value lying within a continuous value range. The charge state of the floating gate then determines, for example, the threshold voltage at which a current flow between two associated electrodes can take place when an electrical voltage is applied to the electrodes.
In accordance with an additional feature of the invention, at least one of the analog characteristics of the analog unit, in particular a threshold voltage of a transistor with a floating gate, is measured and, if necessary, is corrected during and/or after the feeding or extraction of the electrical charge. The measurement can be carried out during the configuration step or after it. In any case, this permits the set state to be checked and, if necessary, to be corrected.
In accordance with another feature of the invention, the circuit configuration has means for connecting and/or disconnecting circuit elements, for example switching elements having one or more switching transistors. This corresponds to the conventional concept which is applied in FPGAs. In combination with the present invention, this results in a large number of possible ways of configuring a circuit configuration with an analog unit. In the extreme case, individual components are available whose analog characteristics can be set in accordance with the invention, and sufficient switching means and line connections are provided in order to be able to set virtually any desired circuit. The significant advantage as compared with conventional concepts is that only a limited, comprehensible number of circuit elements of a specific type have to be provided, since it is certain that the analog characteristics of the circuit elements can be set.
The method can be used with particular advantage in the design of microelectronic circuit configurations. This is because, in the case of a configurable microelectronic circuit configuration the invention permits analog electrical characteristics to be set reversibly and the circuit design to be tested. In the event of a successful test, a further circuit configuration having the same, but unchangeable, analog characteristics can then be produced, for example in mass production. Design errors in the further circuit configuration can therefore be avoided.
As an example of a component whose analog characteristics can be configured in the manner described, mention should be made here of a circuit element having a floating gate, in particular a FLOTOX (floating gate tunneling oxide) element. In a FLOTOX, the charging or discharging of the floating gate is effected by using the tunnel effect. To this end, it is most often the case that a voltage which is unusually high as compared with the operation of the component is applied, so that charge carriers can tunnel with a high probability through the isolating regions surrounding the floating gate. However, the invention is not restricted to the use of the tunnel effect. Instead, other methods for changing the charge state of a floating gate, known from the prior art, can be applied.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a system that includes a microelectronic circuit configuration having an analog electronic unit. The analog electronic unit has an electrically insulated region with an electrical charge state that determines the analog electrical characteristics of the analog electronic unit. The configuration also includes a setting device for setting the electrical charge state to a freely selectable charge value lying within a continuous value range.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a method of using a microelectronic circuit element to set analog characteristics of a circuit configuration. The method includes steps of: providing a circuit configuration having at least one analog electronic unit; providing a microelectronic circuit element having a floating gate for setting analog characteristics of the circuit configuration; and changing a charge state of the floating gate to set the analog characteristics of the circuit configuration.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method, a system, and a method of using a component for setting the electrical characteristics of microelectronic circuit configurations, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.